The present invention relates to a sealing material and, in particular, to a sealing material for use in sealing joints in aircraft.
In the manufacture of an aircraft it is necessary to provide fluid-tight sealing in many of the joints between components, for example, to prevent fuel leakage from fuel tanks or air from pressurised cabins and to prevent water ingress into joints and consequent corrosion in those joints. Joints between components of an airframe are known as interfay joints.
The requirements for sealants used in aircraft include resistance to fuel and water, chemical compatibility with the metals and coatings used in the aircraft components and reliable maintenance of sealing performance over a wide temperature range and over the lifetime of the aircraft.
Polysulphide sealants are known for use in a range of sealing applications and, in particular, are known for use in sealing airframe interfay joints. The polysulphide sealant is typically cured via an oxidative mechanism promoted by a transition metal oxide, for example, manganese dioxide or dichromate compounds or via an organic chemical reaction, for example, epoxidation or condensation esterification. In general, the polysulphide sealants currently used in aircraft manufacture are two-component systems, with the mixing of the components being done shortly before use of the sealant (one-component polysulphide sealants are known but do not, in general, meet the demanding requirements for use in aircraft).
In aircraft manufacture, the components to be assembled into the joint will usually be of lightweight aluminium or titanium alloys or fibre-reinforced composite materials and will usually be painted prior to assembly. The joining or mating faces are first prepared by cleaning with a suitable solvent, light abrasion and wiping dry. Freshly mixed sealant is then applied directly on to at least one mating face and the components are offered together and then fastened with bolts or the like. That known method of joint assembly suffers from a number of disadvantages, including:                the premixing of the sealant components prior to use is labour-intensive, messy and requires accurate control and measurement of the levels of curing promoter in order to ensure that the period during which the sealant remains workable (the “work life”) is sufficient for the planned joint assembly;        the work life and the time required to cure the sealant both depend, inter alia, on the local conditions, in particular, humidity and temperature;        application of the correct amount of liquid sealant requires skill and experience;        the joint must not be disturbed until the sealant is cured which in practice may mean that no further work can be carried out on the components for a period of several days or weeks; and        during tightening of the bolts, the liquid sealant is squeezed away from the immediate vicinity of each bolt thereby allowing direct contact of the components such that subsequent relative movement of the components during the lifetime of the aircraft can cause the paint to rub off, leaving the joint vulnerable to corrosion (this is known as “fretting”).        
There exists a need for improved sealing materials and improved methods of joint assembly to overcome or mitigate some or all of the above-mentioned problems.